The present invention relates to a valve actuator and particularly to a valve actuator for use underwater.
Underwater valves may be operated by valve actuators which are used to open or close the valves in a slow controlled manner. However, it may be necessary to quickly close or open a valve, for example, in an emergency, or on loss of power, instead of in the slower controlled manner.
Typical valve actuators which can close a valve in an emergency have a drive mechanism for opening the valve in a controlled manner and springs for causing the valve actuator to rapidly close the valve. The drive mechanism energises the springs as the valve is opened by compressing the springs so that they store energy to operate. However, a problem with these actuators is that although the springs are energised by the drive mechanism, the drive mechanism also works against the springs during each complete valve operating cycle causing high power consumption.
DE-A-19650947 discloses a valve actuator with a housing and first and second co-axial actuating members coupled together by an axial coupling within the housing, the second actuating member being connected to a plunger valve. A motor on the outside of the housing drives the first actuating member via gearing transmission and hence causes the coupled second actuating member to be moved so as to open or close the plunger valve in a controlled manner. Within the coupling, a spring connects a first coupling member which is fixed to the end of the first actuating member, to a second coupling member which is fixed to the second actuating member. The spring is kept in a compressed state by latches in the first coupling member engaging an annular groove in the second actuating member, the latches being held in place by an electromagnet. If power supply fails, the electromagnet causes the latches to disengage from the groove, and hence causes the second actuating member to be moved by the released spring to close the plunger valve.
DE-A-19516054 also discloses a valve actuator with a housing. Inside the housing is a motor which drives a spindle to open or close a valve in a controlled manner. The motor is slidably mounted within the housing and is fixed to a plunger which is received by an electromagnet in the housing. The motor is also connected to the housing by a spring. The spring is kept in a compressed state by the electromagnet holding the plunger. In the event of power failure, the electromagnet releases the plunger causing the motor and spindle to be moved by the released spring, to close the valve.
It is therefore an object of the present invention to provide a valve actuator for operating a valve in a controlled manner, which can also rapidly close or open a valve and which removes the above mentioned problem.
According to one aspect of the present invention there is provided a valve actuator comprising:
a housing;
an actuating member partly contained within the housing and movable relative to the housing;
drive means arranged to drive the actuating member between first and second positions to reconfigure a valve between first and second states;
energisable resilient means within the housing;
locking means for locking the resilient means in an energised state, the locking means permitting the drive means to drive the actuating member from either of its positions to its other position without substantially energising or de-energising the resilient means when the resilient means is locked by the locking means;
release means for releasing the resilient means from the locking means, to cause the actuating member to be moved under the influence of de-energisation of the resilient means to one of its positions and thereby reconfigure the valve from one to the other of its states; and
the locking means includes the load transfer means which is slidably mounted about the actuating member; and
the resilient means is arranged to be energised by the drive means operatively engaging the actuating member and moving the load transfer means relative to the housing and the actuating member to a position in which the locking means can lock the resilient means in an energised state.
The resilient means are used to close or open a valve in an emergency. The resilient means may comprise at least one spring which is arranged to be energised and locked in place by the locking means, allowing the valve to be subsequently operated without working against the or each spring. This results in a valve actuator having a low power consumption.
The housing may substantially contain the drive means, the resilient means, the locking means and the release means.
It may be desirable for the actuating member to have a stop for engaging the housing, the drive means causing the resilient means to be energised when the stop has engaged the housing.
The load transfer means may comprise a piston like member. The drive means may be rigidly connected to the load transfer means.
It may be desirable for the locking means to comprise at least one movable bolt held substantially within carrier means rigidly connected to the housing. The locking means may comprise bolt engaging means for engaging said at least one bolt, said bolt engaging means being connected to the release means and being slidably mounted within the housing. The locking means may comprise at least one recess in the load transfer means, the or each recess arranged to receive at least one bolt forcibly engaged by the bolt engaging means to lock the resilient means in an energised state. There may be a plurality of bolts, and the carrier means may comprise radially disposed guides, each guide containing one of the bolts and each bolt being radially displaceable. The bolt engaging means may comprise wedging means or annular frusto-conical wedge.
The release means may include a first release part connected to the bolt engaging means and displacable with respect to the housing, and a second release part fixed with respect to the housing, the first and second release parts arranged to be biasable towards each other. The first and second release parts desirably comprise an electromagnet and material attractable to the electromagnet when the electromagnet is magnetised.
Conveniently, the drive means operably engages the actuating member by threaded engagement means. The actuating member may have a screw shaft and the drive means may have threaded means for engaging the screw shaft so as to drive the actuating member. The threaded means may comprise rolling elements for engaging the screw shaft. The drive means may include a rotary motor which drives the threaded means and surrounds the screw shaft. The rotary motor may be rigidly connected to the inside of the piston like member.
The valve actuator may be operable underwater.
According to another aspect of the present invention there is provided a method of operating a valve actuator, comprising an actuating member partly contained within a housing, comprising the steps of:
biasing load transfer means displaceably mounted within the housing relative to the housing by resilient means within the housing;
locking the resilient means in an energised state;
driving the actuating member by drive means between first and second positions to reconfigure a valve between first and second states without substantially energising or de-energising the resilient means; and
releasing the resilient means from being locked, causing the actuating member to be moved under the influence of de-energisation of the resilient means to one of its positions and thereby reconfigure the valve from one to the other of its states; characterized by the steps of
slidably mounting the load transfer means about the actuating member within the housing; and
operatively engaging the actuating member with the drive means to move the load transfer means relative to the housing and the actuating member to energise the resilient means before the locking step.